1. Field of the Invention
The present invention relates to color printers, and more particularly to color printers to the dot matrix impact type in which the different color zones of an ink ribbon are successively impacted to provide printing in color.
2. History of the Prior Art
It is known to provide a color printer of the dot matrix impact type in which the different color zones of an ink ribbon are impacted in succession to provide printing in color. Examples of such a printer are provided by U.S. Pat. Nos. 4,289,069 and 4,336,751 of Melissa et al. The Melissa et al patents describe a color printer having an ink ribbon the length of which is basically divided into three different color zones. Printing in color is accomplished by advancing a first one of the color zones of the ribbon to a print station between a platen and a bidirectionally reciprocating shuttle assembly containing impacting hammers. A page or other document of convenient length is then printed in the color contained in the first zone of the ink ribbon. Tractor drives are employed to advance the print paper in a first direction through the print station as the page is printed in the first color. Following printing of the page in the first color, paper advancement is reversed to return the page in preparation for the printing thereof using the second color zone of the ink ribbon which is advanced into the print station. Following printing of the page in the second color, the paper is again reversed in preparation for printing the page in a third color using the third color zone of the ribbon which is advanced into the print station. By using different combinations of colors and the dots that are printed therefrom, a multi-color printing can be accomplished.
Despite the fact that multi-color printing is provided, the color printer described in the previously referred to Melissa et al patents suffers from a number of disadvantages. One such disadvantage relates to the arrangement of color zones on the ink ribbon. It has been found that the best results are achieved if printing is carried out starting with the lightest color and then proceeding through the increasingly darker colors. If the darker colors are printed first, there is a tendency for the darker ink already deposited on the print paper to rub off onto and thereby contaminate the lighter color zones of the ribbon as such lighter color zones are used for printing. In the three zone ribbon shown and described in the Melissa et al patents, it is simple enough to arrange the colors of the three zones so that the three colors go become progressively darker as the ribbon is advanced along the length thereof in a given direction. However if the ribbon is then driven in the opposite direction, the reverse becomes true and the darkest colors are presented first. The same problem exists where the basic three color pattern is repeated a plurality of times along the length of the ribbon. Again, the desired order of color presentation is achieved in one direction of ribbon movement, but the reverse is true in the opposite direction. It is desirable that the ribbon be driven bidirectionally from end to end during printing in order to optimize speed and efficiency. However, the three color zone ribbon arrangement of the Melissa et al patents is limited to ribbon advancement in a single direction if contamination thereof is to be minimized.
Accordingly, it would be desirable to provide a multi-color ribbon in which the lighter color zones are presented first followed by the darker color zones in either direction of ribbon drive.
In the printer shown and described in the previously referred to Melissa et al patents the ribbon is fed from one reel onto a second reel. Initially, the ribbon is entirely wrapped around the first reel. It is then driven in a first direction until it is substantially completely wound around the second reel, whereupon the direction of driving is reversed and the ribbon is fed from the second reel back onto the first reel. The ribbon typically extends through a path between the opposite reels including various guides. As the ribbon is wound onto either of the reels, portions of two different adjacent color zones are disposed in contact with or at least adjacent to one another. It has been found that in time the ink from one color zone can bleed into portions of the adjacent color zone and vice versa, causing contamination of the ribbon. It has also been found that ink from the various color zones tends to be transferred onto the various guides within the ribbon path. Such ink can then rub off onto color zones of different color, resulting in contamination of the ribbon.
Accordingly, it would be desirable to provide an ink ribbon in which contamination of the various color zones as a result of winding or storage of the ribbon on each of the opposite reels is minimized or eliminated. It would furthermore be desirable to provide a ribbon capable of cleaning some or all of the ink from the guides in the ribbon path so as to minimize or eliminate contamination of the ribbon.
In the color printer shown and described in the previously referred to Melissa et al patents the different color zones of the ribbon which are typically welded together to form the ribbon are identified using an arrangement which includes apertures that are provided in the opposite edges of the ribbon. In this way the printer is capable of identifying the particular color being presented at the print station at any given moment. However, while the arrangement of apertures is capable of identifying the different color zones, it may be desirable to provide a simpler and more reliable arrangement for identifying the color zones utilizing indicia which is easily added to the ribbon in conjunction with a standard coding scheme. It would also be desirable to provide a ribbon which does not have welds or other joints therein which are prone to breaking.
As previously discussed in connection with the color printer shown and described in the Melissa et al patents the ribbon therein is advanced in a given direction so as to present each of three different color zones of the ribbon to the print station in succession. It has been found that the resulting single pass made through each of the color zones can result in a relatively short ribbon life because of the uneven depletion of the ink that can result. For example, the ribbon may be driven at a speed that provides a single pass of a given color zone through the print station during the time required to print a complete page. However, if a number of pages are printed in which only the first portion of each page contains printed matter, then only the corresponding first portion of each color zone on the ribbon is used. This results in depletion of the ink at the first such portion of each color zone while the remaining portion of each color zone experiences little or no ink depletion. An arrangement capable of making ribbon use and the resulting ink depletion more uniform could result in greatly prolonged ribbon life. Furthermore, a single pass through each color zone does not always lend itself to fast and efficient operation, particularly where only portions of the pages contain printed matter and the printer must await advancement of the ribbon to the next ribbon zone at some nominal ribbon driving speed.
In color printers such as of the type shown and described in the previously referred to Melissa et al patents, it is necessary to reverse the paper advancement after a page is printed in a first color so that the same page can be printed in the remaining colors. One approach is to use pairs of conventional tractor drives both above and below the print station. This achieves bidirectional paper advancement rather successfully but at the expense of requiring two separate pairs tractor drives. In this connection it would be desirable to provide a paper driving arrangement in which only a single pair of tractor drives is required, while at the same time the paper is advanced bidirectionally under a desired amount of tension so as to maintain the desired tautness and alignment thereof. This should be done without risk of the smearing of ink on the already printed portions of the paper.